The adverse impact on development productivity of requiring programmers to navigate along access paths to reach target data [...] was enormous. In addition, it was not possible to make slight changes in the layout in storage without simultaneously having to revise all programs that relied on the previous structure. [...] As a result, far too much manpower was being invested in continual (and avoidable) maintenance of application programs.

The most important motivation for the research work that resulted in the relational model was the objective of providing a sharp and clear boundary between the logical and physical aspects of database management.

It is no surprise that attempts such as those of CODASYL and ANSI to develop data structure language (DDL) and data manipulation language (DML) in separate communities have yielded many misunderstandings and incompatibilities.

Relational processing entails treating whole relationships as operands. Its primary purpose is loop-avoidance, an absolute requirement for end users to be productive at all, and a clear productivity booster for application programmers.

For his fundamental and continuing contributions to the theory and practice of database management systems. He originated the relational approach to database management in a series of research papers published commencing in 1970. His paper "A Relational Model of Data for Large Shared Data Banks" was a seminal paper, in a continuing and carefully developed series of papers. Dr. Codd built upon this space and in doing so has provided the impetus for widespread research into numerous related areas, including database languages, query subsystems, database semantics, locking and recovery, and inferential subsystems.

I could imagine how those queries would have been represented in CODASYL by programs that were five pages long that would navigate through this labyrinth of pointers and stuff. Codd would sort of write them down as one-liners. … They weren't complicated at all. I said, "Wow." This was kind of a conversion experience for me.

Don Chamberlin, co-inventor of SQL; quoted in IBM Research News (obituary), April 2003[3]